Process of purifying annealing gases



March 28, 1939. H. D. HOLLER 2,151,764

PROCESS OF PURIFYING ANNEALING GASES Filed DEC. 51, 1956 m m 3 m m a;IIIIIIIIIIIIIIIQEEWIIIIIIIIIIIIIIIIIA (111111111111llllllllllllln-7lllllllllllnr1 h. I

7b f/ecfr/t Supp wxmasses; INVENTOR j Home/D Hal/er:

Patented Mar. 28, 1939 1 UNITED STATES PATENT OFFICE I raocnss or riiigrlr zc ANNEAIilNG 2 East Pittsburgh, Pa., a corporation of sylvaniaPenn- Application December 31, 1936, Serial No. 118,553

2 Claims.

This invention relates to a process for purifying annealing gases. I

In bright annealing stainless steel, it is necessary to remove theoxidizing impurities from the 5 annealing gas to prevent oxidation ofthe surfaces of the steel.

In the processes employed heretofore in purifyingan annealing gas, suchas nitrogen, hydrogen or dissociated'ammonia, the gas is usually sub- Ojected to the action of a dryer or desiccant to remove the water vaporand oxygen sometimes found in the gas. 'These processes haveobjectionable features, for example, it is not always possible to sopurify the gas that it can be employed in bright annealing stainlesssteel without introducing oxidizing impurities, or the purifyingelements employed are too expensive for general commercial use. I

An object of this invention is the provision of a process, forinexpensively purifying annealing gases.

Another object of this invention is to so purify an annealing gasselected from the group comprising nitrogen, hydrogen and mixturesthereof that it may be utilized in bright annealing stainless steelwithout introducing oxidizing impuri- Other objects of this inventionwill become apparent from the following description when so taken inconjunction with the accompanying drawing, the single figure of which isa view partly in section and partly in side elevation of apparatussuitable for practicing this invention.

Referring to the drawing, the apparatus for practicing this inventioncomprises a purifying apparatus l0 suitable for so purifying annealinggases, such as nitrogen, hydrogen and mixtures thereof, for example,dissociated ammonia, that the gases may be employed in bright annealingstainless steel without introducing oxidizing impurities. -In practice,the apparatus l0 may be connected between some suitable source ofannealing gas and an annealing chamber (not shown). I

'As illustrated in the drawing, the annealing gas may be supplied fromany suitable source of supply, such as a storage tank l2. The flow ofthe annealing gas may be controlled by means of a valve l4 disposed inthe pipe line l6 connecting the source of supply with the purifyingapparatus. The apparatus comprises a substantially U-shaped container l8having a cover plate so fltted and. secured thereto by means of bolts 22as to make the purifying apparatus substantially air-tight. The legs ofthe U-shaped container formchambers 24 and 23, the purpose of which willbe explained hereinafter, while the bridge of the U-shaped containercooperates with the cover plate 20 to provide a constricted connectingpassage 28 between'the chambers 24 and 5 26. Packing glands 30 and 32may be disposed in suitable openings in the cover plate 20 for receivingthe connecting pipe line I6 from the source of supply l2 of theannealing gas and a supply p pe 34, respectively. The supply pipe 34connects the chamber 26 of the purifying apparatus with an annealingchamber (not shown).

In practice, a metal 36, which upon heating will vaporize and react withoxidizing impurities in the annealing gas to form metallic oxides, isdisposed in the chamber24 of the U-shaped container. Metals which havebeen found suitable for such vaporization and reaction with theoxidizing impurities are zinc and cadmium.

.In order to heat the metal 36 to a temperature above its melting pointto effect vaporization, a

heater 33, which in the apparatus illustrated is an electrical heatingelement, is disposed to substantially enclose the lower end of thechamber 24. The heating element may be connected to some suitable sourceof electrical supply (not shown). In order to regulate theheat suppliedto the metal during the operation of the purifying apparatus, and tomaintain the temperature high enough to insure the vaporization of themetal, some suitable thermionic element (not shown) may be connected inthe heater circuit and disposed to respond to predetermined temperaturesofthe metal 36 in the chamber 24 to control the operation of the heater38. The heat supplied to the metal 36 will depend upon the metalemployed, since zinc has a melting point of about 419.4 C. and a boilingpoint of about 907 0., while cadmium has a melting point of 320.0 C. anda boiling point of about 767C.

In operation the metalin the chamber 24 is heated to a selectedtemperature between its melting point and boiling point in order toevolve metallic vapors. An annealing gas, such as nitrogen, hydrogen ordissociated ammonia, is supplied to the chamber from a suitable sourceof supply, such as the tank i2. When the annealing gas is admitted tothe chamber 24, it contacts the metallic vapors and a reaction occursbetween the metallic vapors and any oxidizing impurities, such as watervapor or oxygen, which may be present in the annealing gas to formeither zinc oxide or cadmium oxide depending upon the metal employed inthe purifying apparatus.

After the oxidizing impurities have been re- 55 moved from the annealinggas, the purified gas flows through the constricted passage 28 into thecooling chamber 26 where it is cooled to approximately room temperature.The cooling of the gases in the chamber 26 may be effected bydissipating the heat from the chamber by radiation and convection or bysome suitablerefrigerating means. (not shown). If there is an excess ofmetallic vapor in the chamber 24, the unreacted vapors may also flowthrough the constricted passage into the cooling chamber 26 where theunreacted vapors are condensed and solidified on the sides and 'bottomof the container, as illustrated at 40. The purified and cooledannealing gas in the chamber 26 is delivered directly to the annealingchamber (not shown) through the supply pipe 3!.

Where it is desired to employ the process in a recirculating system, thegases from the annealing chamber should be partially purified by meansof known dryers or desiccants before admission to the purifyingapparatus. This is because the present process is more efiicient in sopurifying an annealing that it may be utilized in bright annealingstainless steel without introducing oxidizing impurities when most ofthe impurities have been removed by other means, such as the well knowndesiccants. By removing most of the im.- purities from annealing gasesdrawn directly from an annealing chamber prior to treating the gas bythe present process, the metallic vapors utilized by this process toremove the oxidizing impurities are not contaminated with the largequantities of oxidizing impurities normally found in the furnaceannealing gases.

The process of this invention is very efficient for removing the smallquantities of oxidizing impurities found in annealing gases after theyhave been subjected to known purifying processes and the gases subjectedto this process are suitable for bright annealing stainless steel.Further, since the metals zinc and cadmium are comparatively inexpensiveand since the metallic oxide formed by the reaction between the metallicvapors and the small quantities of oxidizing impurities in the gas arereadily reclaimed, an inexpensive process is provided for purifying theannealing gases, such as nitrogen, hydrogen and dissociated ammonia. Inaddition to being inexpensive, the process may be easily controlled bycontrolling the temperature at which the metallic vapors are produced.

I claim as my invention:

1'. A.process of purifying an annealing gas to provide a non-oxidizinggas for bright annealing stainless steel comprising thesteps of, heatinga metal of the group consisting of zinc and cadmium in a substantiallyair-tight container at a temperature of between the melting point andboiling point of the metal to vaporize it, deliveringan annealing gasselected from the group consistlng of nitrogen, hydrogen and dissociatedammonia into the metallic vapors whereby the metallic vapors react withthe gas to remove oxidizing impurities from the gas, the reactionproduct of the metallic vapors and the oxidizing impurities being stablein each of nitrogen, hydrogen, and dissociated ammonia, providing forthe flow of the gas from the heating and reacting chamber into a coolingchamber wherein the gas and any metallic vapors carried therein are socooled as to free the gas from the vapors by condensing them, andwithdrawing the cooled and purified gas from the cooling chamber.

2. A process of purifying an annealing gas to provide a non-oxidizinggas for bright annealing stainless steel comprising the steps of,heating zinc in a substantially air-tight container at a temperature ofbetween about 420 C. and about 907 C. to vaporize it, delivering anannealing gas selected from the group consisting of nitrogen, hydrogenand dissociated ammonia into the zinc vapors whereby the vapors reactwith the gas to form vaporous zinc oxide thereby removing oxidizingimpurities from the gas, the zinc oxide being stable in each ofnitrogen, hydrogen and dissociated ammonia, providing for the fiow ofthe gas from the heating and reacting chamber into a cooling chamberwherein the gas and any zinc vapors carried therein are so cooled as tofree the gas from the vapors by condensing them, and withdrawing thecooled and purified gas from the cooling chamber.

HOMER. D. HOLLER.

